1. Field of the Invention
The present invention relates to a method for repairing opaque defects (remaining defects) in metal film patterns on a photomask used as an original form in a photomechanical process during manufacture of semiconductor devices (LSIs), and to the structure of the metal film patterns repaired on the photomask.
2. Description of the Background Art
A photomask is used as an original form when transferring resist patterns onto wafer surfaces with a transfer apparatus in a photomechanical process during manufacture of semiconductor devices, on which patterns corresponding to the resist patterns are formed with metal film of CrON etc. If the metal film pattern has residue of the metal film (opaque defects) or blanks of the metal film (clear defects or pinhole defects) differing from the originally designed pattern, then the pattern transferred to the wafer may, depending on the defect size, differ from the originally designed resist pattern or the dimensions of the transferred pattern may vary from those of the original pattern. Furthermore, with the size reduction of the integrated circuit patterns to be finally produced by using the resist as a mask, the dimensional precision required for the resist pattern is becoming more severe, and accordingly the defect size limit allowed on the mask is becoming smaller. When defects exist in the metal film pattern on a photomask, the allowable defect size is usually limited to one-fourth to one-third of the design pattern dimensions (on the mask) so that the defects are not transferred onto the wafer or so that the transferred defects will not cause variation in dimensions from those of the original resist pattern or integrated circuit pattern over a permissible range determined on the basis of the semiconductor product""s quality. Accordingly, while the allowable defect size on a mask was about 1 xcexcm in a semiconductor product with about 3-xcexcm design pattern dimension, the allowable defect size is reduced to about 0.3 xcexcm when the integrated circuit pattern is downsized and the design pattern dimension is reduced to about 1 xcexcm.
A conventional method for repairing opaque defects on the photomask will now be described referring to the plane views of FIGS. 28 and 29. As shown in FIG. 28, the opaque defects include isolated defects (hereinafter referred to as isolated opaque defects) like that shown by 73 and defects continuous with one of the edges of the original metal film pattern 70 (hereinafter referred to as opaque extension defects) like that shown by 72. A laser repair method using YAG (yttrium/aluminum/garnet) laser etc. is usually used to repair such opaque defects 72 and 73. That is to say, as shown in FIG. 29, a laser light beam is shaped through an aperture (not shown) in accordance with the size and shape of the opaque defects 72 and 73 and applied to the opaque defect portions. Then the opaque defects 72 and 73 absorb energy of the laser light and they thus evaporate and disappear. Particularly, for repair of the isolated opaque defect 73, a laser irradiation region 74 is set to sufficiently include the entire defect and the laser light beam is applied to the inside of the region 74 to completely remove the isolated opaque defect 73. For repair of the opaque extension defect 72, the laser light is applied in the same way as in the case of the repair of the isolated opaque defect 73 so that the opaque extension defect 72 can be completely removed. Particularly, for the opaque extension defect 72, the optical system on the optical path is adjusted so that the boundary along which the opaque extension defect 72 is in contact with one edge of the pattern 70 can reproduce the original edge of the pattern defined in the absence of the opaque extension defect 72, and the laser light is applied with one end of the laser irradiation region 74 aligned with the extension of the original pattern edge. That is to say, the original pattern edge is reproduced without allowing the metal film to remain in the repaired area after the opaque extension defect 72 is repaired with laser, or without causing the edge in the repaired area to be recessed from the position of the original pattern edge by excessively removing the metal film. The above-described repairing method is applied to common photomasks mainly using CrON film and also to phase shift photomasks mainly using CrON film or MoSiON film.
The methods for repairing opaque extension defects also include, as well as the laser repair method, a method using ion beam (ion beam etching method), where the beam can be positioned more accurately than in the laser light repair method. In this repair method, as in the case of the laser repair method, the defects are repaired to reproduce the original pattern edges without allowing the metal film to remain in areas where opaque extension defects have been repaired and without causing the repaired areas to be recessed by excessive repair.
The conventional laser repair method or ion beam etching method raise the following problem in the repair of opaque defects. The problem will now be described referring to the plane views of FIGS. 30 and 31.
That is to say, in the areas 75 in FIG. 30 in which the opaque defects have been repaired (opaque defect repaired portions), a very thin film of light-shielding metal remains or the surface of the quartz glass is roughed by the irradiation of beam. Accordingly, the transmittance in the opaque defect repaired portions 75 is lower than that in the original quartz glass portions 71 (FIG. 28) where no opaque defect exists. Hence, when the metal film pattern is transferred onto a semiconductor wafer after the photomask is repaired to form a resist pattern, the exposure to the resist areas located right under the opaque defect repaired portions differs from (is smaller than) the exposure to the other resist areas located right under the original quartz glass portions free of opaque defect. Then, as shown in FIG. 31, parts of the edges of the resist pattern 76 on the semiconductor wafer swell, which raises the problem of dimensional variation of the pattern 76. Such dimensional variation does not cause serious problem in device quality if the devices have such large design pattern dimensions on photomasks, e.g. about 3 xcexcm, as would allow large dimensional variation. However, when the design pattern dimension on photomasks is reduced to about 1 xcexcm, for example, the dimensional variation of the resist pattern due to the transmittance reduction in areas where opaque defects have been repaired by the conventional method seriously affect the device quality over the permissible range. This problem is likely to happen in areas in which isolated opaque defects existing near the metal film pattern have been repaired or in areas where opaque extension defects continuous with edges of the metal film patterns have been repaired. Especially, this problem is very likely to occur in memory cells in DRAM etc. where finest patterns are formed densely.
A first aspect of the present invention is directed to a method for manufacturing a photomask comprising a quartz glass and a pattern composed of a metal film formed on a surface of the quartz glass. According to the present invention, the method comprises the steps of: detecting whether the pattern has an opaque defect continuous with or proximate to the pattern and having a first width in a first direction and a second width in a second direction, the second direction being perpendicular to the first direction and corresponding to a direction in which an edge of the pattern is extended; and when the opaque defect is detected in the step of detecting, removing the opaque defect by applying a given beam onto a beam irradiation region obtained by correcting in the first direction an irradiation region on the surface of the quartz glass which contains the opaque defect and has third and fourth widths respectively in the first and second directions on the basis of a quantity of bias offset of repairing, wherein the quantity of the bias offset is set in accordance with an output condition of the given beam, the dimension in the first direction of a region on the surface of the quartz glass where the opaque defect exists, and size of the opaque defect so that, when the pattern is transferred onto a semiconductor substrate to form a resist pattern by using the photomask obtained after the step of applying the given beam, the rate of dimensional variation of the resist pattern with respect to original dimension of the resist pattern to be obtained in the absence of the opaque defect falls within a given range, and when the quantity of bias offset of repairing has a minus sign, the given beam is controlled so that the beam irradiation region is given as a region including the irradiation region and a pattern repaired region extending into the pattern in the first direction by the absolute value of the quantity of the bias offset, from a boundary between the opaque defect and the pattern when the opaque defect is continuous with the pattern, and from a part facing to the opaque defect in the edge of the pattern when the opaque defect is proximate to the pattern.
Preferably, according to a second aspect of the invention, in the photomask manufacturing method, the pattern repaired region has, in the second direction, a width larger than the second width.
Preferably, according to a third aspect of the invention, in the photomask manufacturing method, the quantity of bias offset of repairing corresponds to an optimum quantity of the bias offset, and the optimum quantity of the bias offset is a quantity of the bias offset which is set when the rate of dimensional variation is 0%.
Preferably, according to a fourth aspect of the invention, in the photomask manufacturing method, when the quantity of bias offset of repairing has a plus sign, the given beam is controlled so that the beam irradiation region is given as a region obtained by narrowing the irradiation region in the first direction by the absolute value of the quantity of the bias offset.
Preferably, according to a fifth aspect of the invention, in the photomask manufacturing method, the pattern is a linear interconnection pattern.
Preferably, according to a sixth aspect of the invention, in the photomask manufacturing method, the pattern has a rectangular opening and the edge of the pattern corresponds to part of the side of the opening.
Preferably, according to a seventh aspect of the invention, in the photomask manufacturing method, the given beam is a laser light beam.
Preferably, according to an eighth aspect, in the photomask manufacturing method, the given beam is an ion beam.
A ninth aspect of the invention is directed to a semiconductor device comprising: a semiconductor substrate; and an integrated circuit pattern obtained on the basis of a resist pattern obtained by transferring the pattern onto the semiconductor substrate by using a photomask manufactured by the photomask manufacturing method of the first aspect.
A tenth aspect of the invention is directed to a semiconductor device comprising: a semiconductor substrate; and an integrated circuit pattern obtained on the basis of a resist pattern obtained by transferring the pattern onto the semiconductor substrate by using a photomask manufactured by the photomask manufacturing method of the fourth aspect.
An eleventh aspect of the invention is directed to a method for manufacturing a photomask comprising a quartz glass and adjacent first and second patterns composed of a metal film formed on a surface of the quartz glass. According to the invention, the method comprises the steps of: detecting whether the patterns have an opaque defect continuous with the first and second patterns and having a first width in a first direction and a second width in a second direction, the second direction being perpendicular to the first direction and corresponding to a direction in which edges of the patterns are extended; and when the opaque defect is detected in the step of detecting, removing the opaque defect by applying a given beam onto a corrected irradiation region obtained by correcting in the first direction an irradiation region on the surface of the quartz glass which contains the opaque defect and has a third width corresponding to the first width and a fourth width respectively in the first and second directions on the basis of a quantity of bias offset of repairing, wherein the quantity of the bias offset is set in accordance with an output condition of the given beam, the dimension in the first direction of a region on the surface of the quartz glass where the opaque defect exists, and size of the opaque defect so that, when the patterns are transferred onto a semiconductor substrate to form resist patterns by using the photomask obtained after the step of applying the given beam, the rate of dimensional variation of the resist patterns with respect to original dimension of the resist patterns to be obtained in the absence of the opaque defect falls within a given range. The quantity of bias offset of repairing has an absolute value equal to a sum of the absolute value of a first quantity of the bias offset and the absolute value of a second quantity of the bias offset, and the beam irradiation region comprises the irradiation region, a first pattern repaired region extending into the first pattern in the first direction by the absolute value of the first quantity of the bias offset from a boundary between the first pattern and the opaque defect, and a second pattern repaired region extending into the second pattern in the first direction by the absolute value of the second quantity of the bias offset from a boundary between the second pattern and the opaque defect.
Preferably, according to a twelfth aspect of the invention, in the photomask manufacturing method, the first and second pattern repaired regions each have, in the second direction, a width larger than the second width.
A thirteenth aspect of the invention is directed to a semiconductor device comprising: a semiconductor substrate; and an integrated circuit pattern obtained on the basis of a resist pattern obtained by transferring the patterns onto the semiconductor substrate by using a photomask manufactured by the photomask manufacturing method of the eleventh aspect.
A fourteenth aspect of the invention is directed to a photomask comprising: a quartz glass; and a pattern composed of a metal film formed on a surface of the quartz glass, wherein part of one edge of the pattern is missing.
Preferably, according to a fifteenth aspect of the invention, the photomask further comprises: another pattern formed on the surface of the quartz glass, composed of a metal film, and adjacent to the pattern, wherein part of an edge of the additional pattern which faces to the one edge of the pattern is also missing.
A sixteenth aspect of the invention is directed to a semiconductor device comprising: a semiconductor substrate; and an integrated circuit pattern obtained on the basis of a resist pattern obtained by transferring the pattern onto the semiconductor substrate by using the photomask of the fourteenth aspect.
According to the first and eleventh aspects of the invention, a reduction in transmittance in the repaired defect portion can be appropriately corrected, so that the dimensional variation on the resist pattern formed by transferring the repaired pattern on the photomask can be restrained within a range permitted for the device quality.
According to the second and twelfth aspects of the invention, the absolute value of the quantity of bias offset of repairing can be set relatively small so that the repaired portion can be prevented from being detected as a defect after the repair of the opaque defect.
According to the third aspect of the invention, the opaque defect is completely removed by the irradiation of beam, part of the pattern in the pattern repaired region is removed together and the quartz glass portion right under it is exposed. Accordingly, when transferring the repaired pattern on the photomask to a resist on a semiconductor substrate, the light is transmitted through the exposed quartz glass portion, by diffraction etc., also upon the resist layer located right under the quartz glass portion from which the opaque defect has been removed (a repaired defect portion). This completely compensates for the reduction in transmittance in the repaired defect portion and the resist layer can be exposed to the light as if the transmittance were not reduced. The resist pattern thus obtained by transfer coincides with the original resist pattern to be obtained.
According to the fourth aspect of the invention, the reduction in transmittance in the quartz glass portion right under the remainder and in the repaired defect portion can be appropriately corrected, so that the dimensional variation on the resist pattern formed by transferring the repaired pattern on the photomask can be suppressed within a range permitted for the device quality.
According to the fourteenth and sixteenth aspects of the invention, when transferring the pattern on the photomask to a resist layer, the light can be transmitted through the missing portion in one edge of the pattern by diffraction etc., upon the resist layer right under the quartz glass portion between adjacent pattern edges to contribute to exposure of the layer. It is thus possible to obtain a semiconductor device in which the dimensional variation on the finally produced resist pattern and the integrated circuit pattern formed on the basis of the resist pattern is suppressed to zero or within a permissible range required in accordance with the design pattern dimensions of the semiconductor device.
The present invention has been made to solve the problems described above, and objects of the present invention are to provide: 1) a photomask manufacturing method which can compensate for reduction in transmittance in an opaque defect repaired portion (particularly an isolated opaque defect existing in area where metal film pattern portions are arranged in close proximity or an opaque extension defect) in a metal film pattern on a common photomask so as to suppress dimensional variation of the repaired portion on the pattern formed on a semiconductor wafer in a photomechanical process, 2) a photomask manufacturing method which can compensate for a reduction in transmittance in an opaque defect repaired portion (particularly an isolated opaque defect existing in an area where metal film pattern portions are arranged in close proximity or an opaque extension defect) in a metal film pattern on a phase shift photomask so as to suppress dimensional variation of the repaired portion on the pattern formed on a semiconductor wafer in a photomechanical process, and 3) the metal film pattern structure on the photomask manufactured by using the method 1) or 2).
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.